1. Field of the Invention
The present invention relates to a Ni-based single crystal super alloy, and more particularly, to a technology employed for improving the creep characteristics of Ni-based single crystal super alloy.
2. Description of the Related Art
An example of the typical composition of Ni-based single crystal super alloy developed for use as a material for moving and stationary blades subject to high temperatures such as those in aircraft and gas turbines is shown in Table 1.
TABLE 1AlloyElements (wt %)nameAlTiTaNbMoWReCZrHfCrCoRuNiCMSX-26.01.06.0—1.08.0————8.05.0—RemCMSX-45.61.06.5—0.66.03.0———6.59.0—RemRene′N66.0—7.00.31.06.05.0——0.24.013.0—RemCMSX-5.70.38.40.10.45.56.3——0.032.33.3—Rem10K3B5.70.58.0——5.56.00.05—0.155.012.53.0Rem
In the above-mentioned Ni-based single crystal super alloys, after performing solution treatment at a prescribed temperature, aging treatment is performed to obtain an Ni-based single crystal super alloy. This alloy is referred to as a so-called precipitation hardened alloy, and has a from in which the precipitation phase in the form of a γ′ phase is precipitated in a matrix in the form of a γ phase.
Among the alloys listed in Table 1, CMSX-2 (Canon-Muskegon, U.S. Pat. No. 4,582,548) is a first-generation alloy, CMSX-4 (Canon-Muskegon, U.S. Pat. No. 4,643,782) is a second-generation alloy, Rene′N6 (General Electric, U.S. Pat. No. 5,455,120) and CMSX-10K (Canon-Muskegon, U.S. Pat. No. 5,366,695) are third-generation alloys, and 3B (General Electric, U.S. Pat. No. 5,151,249) is a fourth-generation alloy.
Although the above-mentioned CMSX-2, which is a first-generation alloy, and CMSX-4, which is a second-generation alloy, have comparable creep strength at low temperatures, since a large amount of the eutectic γ′ phase remains following high-temperature solution treatment, their creep strength is inferior to third-generation alloys.
In addition, although the third-generation alloys of Rene′N6 and CMSX-10 are alloys designed to have improved creep strength at high temperatures in comparison with second-generation alloys, since the composite ratio of Re (5 wt % or more) exceeds the amount of Re that dissolves into the matrix (γ phase), the excess Re compounds with other elements and as a result, a so-called TCP (topologically close packed) phase precipitates at high temperatures causing the problem of decreased creep strength.
In addition, making the lattice constant of the precipitation phase (γ′ phase) slightly smaller than the lattice constant of the matrix (γ phase) is effective in improving the creep strength of Ni-based single crystal super alloys. However, since the lattice constant of each phase fluctuates greatly fluctuated according to the composite ratios of the composite elements of the alloy, it is difficult to make fine adjustments in the lattice constant and as a result, there is the problem of considerable difficulty in improving creep strength.
In consideration of the above circumstances, the object of the present invention is to provide a Ni-based single crystal super alloy that makes it possible to improve strength by preventing precipitation of the TCP phase at high temperatures.